In order to form large containers or conduits whose walls can be heated or cooled, it is known to join large-diameter pipe sections and then to clad the joined sections with a strip that forms with them a helical passage. The strip and pipe sections are formed of a weldable metal, normally steel.
As a rule the pipe sections are secured together by an apparatus which positions two pipe sections adjacent each other with their axes aligned and their ends abutting. The two pipe sections are then normally jointly rotated adjacent a welding tool which seams the two ends together.
Subsequently the joined sections are normally moved to a location where a U-section metal strip is manually wound helically around the joined sections and joined thereto along the strip edges. As a rule the strip is merely temporarily secured to the joined pipe sections, then the entire assembly is heat treated to eliminate stresses, and subsequently the two edges of the strip are welded in continuous seams to the outer surface of the joined pipe sections.
Obviously the cost of making such an item is extremely high. In addition the product is often unsatisfactory, in that the welds joining the U-section strip to the joined pipe sections are relatively failure prone, frequently developing leaks and requiring subsequent expensive repair.